High Compression Downhole Pump

ABSTRACT

A downhole pump has a barrel and a plunger. The barrel has a first one-way valve and the plunger has a second one-way valve. The plunger is of the box end type. The pump prevents or minimizes gas lock by achieving high compression in the compression chamber between the two valves. The second valve is located close to the bottom end of the plunger. In the second valve, the valve seat is in contact with the seat plug, which seat plug has a seal. Alternatively, the valve seat is incorporated into the seat plug, which seat plug also has a seal. The plunger lacks reliefs at the bottom end and thereby achieves tight tolerances with the barrel, further contributing to high compression.

This application claims the benefit of U.S. provisional patentapplication Serial No. 60/909,743, filed Apr. 13, 2007.

FIELD OF THE INVENTION

The present invention relates to subsurface or downhole pumps such asare used to pump oil and other fluids in bases for oil wells.

BACKGROUND OF THE INVENTION

When an oil well is first drilled and completed, the fluids (such ascrude oil) may be under natural pressure that is sufficient to produceon its own. In other words, the oil rises to the surface without anyassistance.

In many oil wells, and particularly those in fields that are establishedand aging, natural pressure has declined to the point where the oil mustbe artificially lifted to the surface. Subsurface, or downhole, pumpsare located down in the well below the level of the oil. A string ofsucker rods extends from the pump up to the surface to a pump jackdevice, or beam pump unit (see FIG. 1). A prime mover, such as agasoline or diesel engine, or an electric motor, or a gas engine on thesurface causes the pump jack to rock back and forth, thereby moving thestring of sucker rods up and down inside of the well tubing.

The string of sucker rods operates the subsurface pump. A typical pump(see FIG. 2) has a plunger that is reciprocated inside of a barrel bythe sucker rods. The barrel has a standing one-way valve, while theplunger has a traveling one-way valve, or in some pumps the plunger hasa standing one-way valve, while the barrel has a traveling one-wayvalve. Reciprocation charges a chamber between the valves with fluid andthen lifts the fluid up the tubing toward the surface.

The chamber between the standing and traveling valves is referred to asthe compression chamber. The standing and traveling valves open andclose by differential pressure. For example, when the plunger is dropped(the downstroke), the fluid in the compression chamber is pressurized bythe plunger. The fluid in the compression chamber cannot escape by wayof the standing valve, because of the one-way nature of the standingvalve. The only escape for the fluid in the compression chamber isthrough the traveling valve. However, in order to open the travelingvalve, the fluid in the compression chamber must be pressurizedsufficiently to overcome the pressure of the fluid above the travelingvalve.

In a well that produces both liquid and gas, the pump can become gaslocked. In a gas locked pump, the compression chamber contains enoughgas to act as a shock absorber, resulting in insufficient differentialpressure to open the traveling valve. When gas locked, the pumpreciprocates without pumping any fluid.

In the prior art, pin end plungers, (which have a pin formed by exteriorthreads at the plunger lower end as shown in FIG. 3), or box endplungers with external valves (see FIG. 4) are used to minimize gaslocking. These plungers use a valve generally attached to the bottom ofthe plunger. This attached valve introduces uncompressible volumes intothe compression chamber, which uncompressible volumes are located aroundthe valve, around the seat plug and internal of the seat plug. Theseuncompressible volumes make it more difficult to achieve a highcompression ratio in order to overcome gas locking.

In another form of the prior art, a box end plunger (see FIG. 4A) isconfigured with an internal valve comprised of an insert, ball, seat,o-ring, spacer, and seat retainer. This arrangement is an improvementover the other prior art but still introduces unnecessary,uncompressible compression chamber volume in the spacer and the externalturned-down length at each end of the plunger. These volumes also makeit more difficult to achieve a high compression ratio in order toovercome gas locking.

Thus, there is a need for a high compression pump that can operate ingas locked wells.

SUMMARY OF THE INVENTION

The present invention provides a downhole pump, which comprises a barreland a plunger. The barrel has a first one-way valve. The plunger hasfirst and second ends, with a passage that extends between the first andsecond ends and a counterbore in each end. A second valve is located inone of the counterbores of the first or second ends. The second valvecomprises an insert with a ball located in the insert, a seat adjacentto the insert, and a seat plug in contact with the seat. The seat plughas a channel therein with a pressure seal in the channel. The seat plugcouples to the inside of the plunger so as to form a box end.

In accordance with another aspect of the present invention, the plungerhas an outside diameter that is substantially the same along its length.

In accordance with still another aspect of the present invention, theplunger is reversible.

The present invention provides a downhole pump, which comprises a barreland a plunger. The barrel has a first one-way valve. The plunger hasfirst and second ends, with a passage that extends between the first andsecond ends and a counterbore in each end. A second valve is located inone of the counterbores of the first or second ends. The second valvecomprises an insert with a ball located in the insert and a seat plug incontact with the seat. The seat plug has a channel therein with apressure seal in the channel. The seat plug has a seat for the ball. Theseat plug couples to the inside of the plunger so as to form a box end.

In accordance with another aspect of the present invention, the plungerhas an outside diameter that is substantially the same along its length.

In accordance with still another aspect of the present invention, theplunger is reversible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a well, shown with pumping equipment.

FIG. 2 is a longitudinal partial cross-sectional view of a downholepump.

FIG. 3 is an exploded view of the lower end of a prior art pin endplunger and valve.

FIG. 4 is an exploded view of the lower end of a prior art box endplunger and external valve.

FIG. 4A is an exploded view of the lower end of a prior art box endplunger and internal valve.

FIG. 5 is a perspective exploded view of the plunger of the presentinvention, in accordance with a preferred embodiment.

FIG. 6 is a perspective view of the assembled plunger of FIG. 5.

FIG. 6A is a perspective view of the lower end of the assembled plungerof FIG. 5, shown cut away.

FIG. 7 is a cross-sectional view of the lower end portion of the plungerof the present invention.

FIG. 8 is a cross-sectional view of the lower end of the prior artplunger of FIG. 4A.

FIG. 9 is a perspective exploded view of the plunger of the presentinvention, in accordance with another embodiment.

FIG. 10 is a perspective view of the assembled plunger of FIG. 9.

FIG. 11 is a cross-sectional view of the lower end portion of theplunger of FIGS. 9 and 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, there is shown a schematic diagram of a producing oil well11. The well has a borehole that extends from the surface 13 into theearth, past an oil-bearing formation 15.

The borehole has been completed and therefore has casing 17 which isperforated at the formation 15. A packer or other method (not shown)optionally isolates the formation 15 from the rest of the borehole.Tubing 19 extends inside of the casing from the formation to the surface13.

A subsurface pump 21 is located in the tubing 19 at or near theformation 15. A string 23 of sucker rods extends from the pump 21 upinside of the tubing 19 to a polished rod at a stuffing box 25 on thesurface 13. The sucker rod string 23 is connected to a pump jack unit 24which reciprocates up and down due to a prime mover 26, such as anelectric motor, a gasoline or diesel engine, or a gas engine.

FIG. 2 illustrates a typical downhole pump 27. In FIG. 2, valve insertsor cages and other details are not shown. The pump 27 has a barrel 29and a plunger 31 which reciprocates inside of the barrel. The barrel 29has a standing valve 33 and the plunger has a traveling valve 35.

The plunger is reciprocated inside of the barrel by the sucker rods 23.As the plunger 31 is raised on the upstroke, fluid is drawn into acompression chamber 37 located between the two valves 33, 35. The fluidcontains liquid 39, such as oil and condensate, and gas 41, such asnatural gas, air or vacuum. The gas 41 may be separated from the liquid39 as shown in the drawing, or it may be in solution with the liquid.

In the prior art, plungers have pin ends or box ends. In a pin endplunger 43 (see FIG. 3), the lower end of the plunger has externalthreads 45. The lower end of the plunger has a bore 53 which extends thelength of the plunger 43. An external valve is attached to the lower endof the plunger. The valve has a cage 55, a ball 57, a seat 59 and a seatplug 49. The cage 55 has internal threads 56 that are threaded onto thelower end threads 45 of the plunger 43. The seat plug 49 retains theball 57 and the seat 59 inside of the cage 55. The seat plug 59 forms ametal-to-metal seal with the cage 55.

In a box end plunger 61 (see FIGS. 4 and 4A), the lower end of theplunger has internal threads for receiving the external threads of thevalve components. FIG. 4 shows a box end plunger 61 having externalvalve components. The valve is similar to that shown in FIG. 3, having acage 55A, a ball 57, a seat 59 and a seat plug 49. The upper end of thecage 55A has exterior threads 67 to engage the interior threads 63 ofthe plunger 61. A passage 71 extends between the two ends of the plunger61. The passage 71 is larger than the passage 53 of the pin end plunger43. In addition, the lower end of the plunger 61 has reliefs 83 machinedtherein to decrease the outside diameter of the plunger at the lowerend. The reliefs 83 compensate for wall movement; when the cage 55A isscrewed into the passage 71, the wall of the plunger lower end bulgesout. The reliefs 83 are 1/32″ deep as measured on the diameter. Thereliefs 83 extend over an inch from the ends of the plunger. The plunger61 is reversible with both ends having reliefs 83 and capable offunctioning as either a top end or a bottom end.

The plungers 43 and 61 (shown in FIGS. 3 and 4, respectively) have anuncompressible space or volume around the outside diameter of the cage55, 55A. Due to the difficulty and expense of manufacturing concentricthreads 56, 67 with the diameter of the cages and of manufacturingconcentric threads 45, 63 with the diameter of the plunger, the cagesare made with a slightly reduced outside diameter. This avoids wear ofthe cage on the barrel. The cages have a reduced outside diameter,relative to the plunger outside diameter, of about 1/32 to 1/16 inches.This gap between the cage and the barrel creates a space or volume thatcannot be compressed. Other uncompressible volumes are around the seatplug 49 and internal of the seat plug.

Still another prior art box end plunger 61A is shown in FIG. 4A. Theplunger 61A has internal traveling valve components. The lower end ofthe plunger has a counterbore 69 which communicates with a passage 71.The passage 71 of the box end plunger is larger than the passage 53 ofthe pin end plunger. The counterbore 69 receives the valve insert 73,the valve ball 75, the valve seat 77 and a spacer 79 with an o-ring seal80. This plunger 61A has uncompressible volumes in the spacer 79, in theexternal turn-downs, or reliefs 83, at the ends, and internal of theseat plug 65.

The present invention provides a pump with a box end plunger that makesthe compression chamber small at the bottom of the downstroke (when thecompression chamber is at its smallest volume), thereby achieving highcompression in the compression chamber 37 (see FIG. 7). The highcompression in turn causes the traveling valve to open even with largeamounts of gas, thereby preventing or minimizing gas lock. The plungeris also suitable for use with heavy crude or in high flow wells.

The plunger 81 of the present invention is illustrated in FIGS. 5, 6 and6A. The plunger 81 is a hollow tube, having a passage 84 therethrough.The plunger has two ends 85; each end has a counterbore 87 formedtherein. At one end, the top end, retainer components are inserted. Atthe other end, the bottom end, traveling valve components are inserted.Each end of the plunger has a reduction in outside diameter of about0.005 inches, extending ⅜ inch from the end, to account for slightswelling of the diameter on the plunger end when the valve componentsare inserted and tightened into the plunger. This reduction in diameteris so small as to be substantially the same as the diameter along theremainder of the plunger, and after the valve components are inserted,the diameters are even more so substantially the same.

The retainer components are a spacer 89 and a retainer 91. The spacer 89is a hollow tube, typically unthreaded. The retainer 91 is also a hollowtube, with external threads 93 on at least one end, which end isthreaded into one of the plunger counterbores 87. The retainer couplesto the sucker rod string 23. The retainer 91 and the spacer 89 can be asingle component as shown, or can be two separate components.

The traveling valve components are a valve insert 95, a valve ball 97, avalve seat 99 and a seat plug 101. The insert 95 is inserted into thecounterbore 87 at one end of the plunger. The insert abuts a shoulder105 (see FIG. 7). The insert 95 has openings 107 (see FIG. 5) in thesides to allow fluid to flow past the ball 97 when the valve is open.The ball 97 is put into the insert 95. The seat 99 then follows so as toabut the bottom end of the insert. The seat plug 101 is inserted intothe counterbore 87. The seat plug 101 contains an o-ring seal 103 thatseals against pressure. Other types of pressure seals can be used, suchas o-rings with backup seals, cup type seals and x-type seals.

The seat plug 101 has exterior threads 109 (see FIG. 7) to engageinterior threads 111 in the counterbore 87. The interior threads 111 ofthe counterbore extend from the open end of the counterbore toward theshoulder 105 for a distance that is substantially the same as thethreaded length of the seat plug 101. The seal 103 contacts anunthreaded, or smooth, surface of the counterbore 87. The seat plug 101,which is a hollow ring, typically has a hexagonal or square shape forthe lower part of its interior bore so as to receive a tool thatinstalls and removes the plug from the plunger end. The seat plug 101has around its inner end a circumferential channel 113. The channel 113receives the o-ring 103. When the seat plug 101 is installed into an endof the plunger, the seat plug contacts the seat 99 and the o-ring 103 iscompressed between the seat plug and the valve seat 99 and forms a seal.Additionally a seal is accomplished in counterbore 87.

Although the channel 113 has been described as between two parts (namelythe seat plug 101 and the seat 99), the channel can be within a singlepart. For example, the channel can be entirely on the seat plug, whereinthe channel takes on the form of a groove.

With the plunger of the present invention, the traveling valve 97, 99 islocated close to the bottom end 1 15 of the plunger. Comparing theplunger 81 of the present invention (FIG. 7) with the prior art box end,internal valve plunger 61 (FIG. 8), the difference in spacing of thevalve seats 99, 77 from the bottom of the plunger is noticeable. The boxend plunger 81 of the present invention is able to achieve highcompression because of the reduced spacing between the traveling valvecomponents and the standing valve components 1 16.

In addition, the plunger of the present invention has minimal or norelief at the bottom end 115. This makes the clearance between theplunger end and the barrel smaller and tighter than the plunger 61A ofFIG. 4A. In addition, the clearance between the plunger end and thebarrel is smaller and tighter than the plungers 43 and 61 of FIGS. 3 and4 which have gaps (due to manufacturing tolerances) between the cagesand the barrel. As a result, the plunger 81 can achieve highercompressions. With a standard conventional plunger, a compression ratioof about 34:1 can be achieved. With the plunger of the presentinvention, a compression rate of about 45:1 can be achieved, an increaseof 33% in compression ratio. If the plunger is used in conjunction witha high compression standing valve, the compression ratio is higherstill.

Furtherstill, the two ends of the plunger 81 are reversible. Each endcan function as either the top end or the bottom end. When the plungeris installed into a downhole pump, the top end will wear faster than thebottom end. The plunger can be pulled from the well and the plungerreversed and reinstalled. What was the bottom end, with little or nowear, is now the top end. The amount of wear relative to the reliefs 83is small by an order of magnitude or so. Thus, a worn top end can beused as a bottom end and still achieve high compression due to tighttolerances with the barrel.

FIGS. 9-11 show the plunger 121 in accordance with another embodiment.In this embodiment, the seat plug functions as both a seat for the valveball and also as a holder for the seal. In the description that follows,like reference numbers designate like parts or components in the variousembodiments.

The box end plunger 121 is similar to the plunger 81 described withrespect to FIGS. 5-7. The plunger 121 has a passage 83 therethrough andtwo ends 85, with each end having a counterbore 87 formed therein. Theplunger 121 is reversible. At one end, the top end, retainer components,in the form of a spacer 89 and a retainer 91, are inserted. At the otherend, the bottom end, traveling valve components are inserted.

The traveling valve components are a valve insert 95, a valve ball 97and a seat plug 123. The insert 95 abuts a shoulder 105 in thecounterbore 87.

The seat plug 123 has a seat 125 for the valve ball 97. The seat plug123 also has a circumferential channel 113 around the inner end. Thechannel 113 receives the seal 103.

The seat plug 123 is a hollow ring, with a square or hex shape for itsinner bore. The seat plug has exterior threads 109 that engage interiorthreads 111 of the counterbore 87.

Assembly involves inserting the insert 95 into the counterbore 87, thenthe ball 97 and then the seat plug 123. The seat plug has the seal 103in the channel 113. When the seat plug 123 is installed and tightenedinto the plunger, the seat plug contacts the insert 95. The seal 103 iscompressed between the insert 95 and the seat plug 123 and forms a seal.When the valve is closed, the ball 97 is in the seat 125, as shown inFIG. 11. When the valve is open, the ball is off of the seat.

Locating the valve seat 125 and the seal 103 on the seat plug 123 servesto further reduce the volume of the compression chamber when the plungeris at the bottom of the downstroke, thereby achieving high compression.The plunger 121 has minimal or no relief at the bottom end to furtherminimize the volume of the compression chamber.

Thus, the present invention provides a box end plunger that achieveshigh compression. Consequently, gas lock of the pump is minimized oreven eliminated. The plunger is reversible to increase wear and usefullife, making the plunger more cost effective to use.

The plunger of the present invention can be used in tubing pumps orinsert pumps. The plunger can reciprocate or the barrel can reciprocate.

The foregoing disclosure and the showings made in the drawings aremerely illustrative of the principles of this invention and are not tobe interpreted in a limiting sense.

1. A downhole pump, comprising: a) a barrel having a first one-wayvalve; b) a plunger having first and second ends, with a passage thatextends between the first and second ends and a counterbore in each end;c) a second valve located in one of the counterbores of the first orsecond ends, the second valve comprising an insert with a ball locatedin the insert, a seat adjacent to the insert, and a seat plug in contactwith the seat, the seat plug having a channel therein with a pressureseal in the channel, the seat plug coupling to the inside of the plungerso as to form a box end.
 2. The pump of claim 1 wherein the plunger hasan outside diameter that is substantially the same along the length ofthe plunger.
 3. The pump of claim 1 wherein the plunger is reversible.4. A downhole pump, comprising: a) a barrel having a first one-wayvalve; b) a plunger having first and second ends, with a passage thatextends between the first and second ends and a counterbore in each end;c) a second valve located in one of the counterbores of the first orsecond ends, the second valve comprising an insert with a ball locatedin the insert, a seat plug in contact with the insert, the seat plughaving a channel therein with a pressure seal in the channel, the seatplug having a seat for the ball, the seat plug coupling to the inside ofthe plunger so as to form a box end.
 5. The pump of claim 4 wherein theplunger has an outside diameter that is substantially the same along thelength of the plunger.
 6. The pump of claim 4 wherein the plunger isreversible.